EP2164752B1 - Underwater buoy with modular members - Google Patents

Abstract

An underwater buoy for hanging a duct between a sea bed and the surface, the buoy including a frame and a plurality of modular members mounted in the frame, the modular members extending between their two opposite modular-member ends, the frame including a longitudinal body for receiving the extended tubular duct, and retainers mounted on the body for maintaining the modular members substantially parallel to the body. The retainers include two retaining structures spaced from each other along the body. The retaining structures are maintained in a fixed position relative to each other in order to hold at least one modular member.

Description

The present invention relates to a submarine buoy with modular elements for suspending the tubular transport of hydrocarbons, between a seabed and a surface installation.

In order to raise the hydrocarbons of a subsea well towards the surface, tubular conduits are installed substantially vertically between the well and an underwater zone located below the surface of the water, then these vertical tubular conduits are prolonged by tubular conduits generally flexible, which join a surface installation. The substantially vertical tubular pipes are generally rigid and are thus maintained vertically through underwater buoys. The size of its underwater buoys and consequently the volume of air that they are likely to trap, must be adjusted according to the upward force they must exert on the tubular pipe in order to maintain it vertically. However, this ascensional effort also depends on the dimensions of this pipe and its length, in other words on the depth of water. In addition, when the upward force to be exerted is relatively important, in parallel, the volume of the underwater buoy must also be important. Also, since it is difficult to carry buoys of large volume, it was imagined to transport them in pieces, for example on the laying boats, and then to climb at sea directly on the site.

Thus, the buoys comprise an armature and modular elements that form floats, and these floats are adapted to be mounted in said frame at the time of installation of the buoy. The modular elements extend respectively longitudinally between two opposed modular element ends. Said armature has a longitudinal hollow body intended to receive said extended tubular conduit, while retaining means mounted radially on said hollow body make it possible to maintain said modular elements substantially parallel to said hollow body and around said hollow body.

We can refer in particular to the document WO 03/064807 which describes such an underwater buoy.

However, when the modular elements are relatively large so that the underwater buoy exerts a relatively high upward force, the retaining means are intensely stressed and may rupture.

Also, a problem that arises and that aims to solve the present invention is to provide a submarine buoy with modular elements whose modular elements are more securely retained by the retaining means so as to prevent breakage of the latter.

In order to solve this problem, the present invention proposes a submarine buoy with modular elements for suspending a tubular pipe between a seabed and a surface, said buoy comprising an armature and a plurality of modular elements forming floats suitable for being mounted in said armature, said modular elements extending respectively longitudinally between two opposite modular element ends, said armature having a longitudinal hollow body for receiving said extended tubular pipe and retaining means mounted radially on said hollow body to maintain said modular elements substantially parallel to said hollow body and around said hollow body; according to the invention said retaining means comprise two retaining structures spaced longitudinally spaced from each other on said hollow body, said retaining structures respectively having a plurality of receiving zones, each being adapted to receive an end d modular element; and said holding structures are held in a fixed position relative to each other in a position where said receiving areas are respectively facing each other so as to trap at least one modular element when said opposite ends of said at least one element modular are respectively engaged in two receiving areas opposite.

Thus, a feature of the invention lies in the mode of cooperation of the two retaining structures, which encircle the modular elements when they are brought into a position close to each other. In this way, when the tubular pipe which rises from the bottom is suspended from the underwater buoy, the latter is oriented so that the hollow body extends substantially vertically as the modular elements. Modular elements that have a density lower than that of seawater, exerts an upward force on one of the two retaining structures which itself is integral with the hollow body. Also, these modular elements abut against this retaining structure, and they are maintained in this position in particular thanks to the other retaining structure.

Advantageously, each modular element is cylindrical in shape with a circular director, so that it can be manufactured industrially and at an advantageous cost. Given the symmetry of the modular elements, their wall resists much better to the hydrostatic pressure despite a relatively small thickness in comparison with a parallelepiped-shaped modular element, for example. Moreover, thanks to this cylindrical symmetry, the modular elements are more easily manipulated in the water when it comes to replace or mount additional modular elements in the frame.

In addition, said retaining means preferably comprise spacers mounted on said hollow body to maintain said modular elements away from said hollow body, the modular elements coming to bear against these spacers. They allow moreover, to stiffen the connections between the modular elements and the hollow body. Furthermore, these spacers respectively have a semicircular recess for receiving said modular element and blocking and the lateral movements of the tubular element in directions substantially parallel to a tangent plane of the hollow body.

According to a preferred embodiment and implementation of the invention, said retaining structures have a central portion secured to said hollow body and radial portions in which are formed said receiving areas. Thus, for example, said retaining structures have eight star-shaped and diametrically opposite two-by-two radial portions, in which eight receiving zones are respectively provided.

Moreover, said retaining structures define an average plane which extends substantially perpendicularly to said hollow body and at least one of said retaining structures, that which is located towards the surface when the underwater buoy is in position, is equipped with means complementary blocking means in said receiving areas for blocking said modular element in all directions substantially parallel to said mean plane. Thus, when the underwater buoy is in the normal working position, the hollow body is oriented vertically and the modular elements, given their lower density than water, tend to rise towards the surface and exert efforts ascensional specifically on said at least one of said retaining structures. Also, thanks to the complementary locking means, in the receiving zones of this retaining structure, which takes up the significant upward forces, the ends of the modular elements are completely integral with the retaining structure. And thus, the modular elements are totally attached to the frame.

Advantageously, said at least one of said retaining structure, located towards the surface, has reinforcing means for increasing the rigidity of said at least one of said retaining structure, so as to better withstand the upward forces produced by the modular elements.

At the opposite end, said hollow body has, in the vicinity of the other of said retaining structures, hooking means to said tubular pipe to take up the forces exerted by the tubular pipe which rises from the seabed and tends to bring the underwater buoy to this bottom. Thus, these forces are directly exerted on the hollow body and they are taken over and compensated by the modular elements through the retaining structure. Of course, said other of said retaining structures, directed towards the seabed, comprises means for locking said modular elements so that they are completely integral with the hollow body.

• la Figure 1 est une vue schématique en perspective d'une armature de bouée sous-marine conforme à l'invention ;
• la Figure 2 est une vue schématique en perspective, d'une bouée sous-marine conforme à l'invention ;
• la Figure 3A est une vue schématique en coupe axiale selon le plan III-III de la bouée sous-marine illustrée sur la Figure 2 ;
• la Figure 3B est une vue schématique en coupe axiale selon un plan vertical d'une bouée sous-marine conforme à l'invention selon une variante de réalisation ;
• la Figure 4 est une vue schématique de dessus selon la flèche IV de la bouée sous-marine représentée à la Figure 3A ; et,
• les Figures 5A à 5C illustrent schématiquement en coupe droite, le montage d'une bouée sous-marine telle que représentée sur la Figure 2.

Other features and advantages of the invention will become apparent on reading the following description of particular embodiments of the invention, given by way of indication but not limitation, with reference to the accompanying drawings in which:

• the Figure 1 is a schematic perspective view of an underwater buoy reinforcement according to the invention;
• the Figure 2 is a schematic perspective view of an underwater buoy according to the invention;
• the Figure 3A is a schematic view in axial section along the plane III-III of the underwater buoy illustrated on the Figure 2 ;
• the Figure 3B is a schematic view in axial section along a vertical plane of an underwater buoy according to the invention according to an alternative embodiment;
• the Figure 4 is a schematic top view along arrow IV of the submarine buoy shown in FIG. Figure 3A ; and,
• the Figures 5A to 5C illustrate schematically in straight section, the mounting of an underwater buoy as shown on the Figure 2 .

The Figure 1 illustrates a frame 10 of underwater buoy according to the invention. This frame 10 comprises a hollow body 12 of a length of between thirty meters and forty meters, for example thirty five meters, and it comprises an upper retaining structure 14 and a lower retaining structure 16. Moreover, spacers 18 which will be described below are installed along the hollow body 12. This hollow body 12, of circular symmetry about an axis A, has an upper end 20 and a lower end 22 and its relatively constant diameter is between one meter and two meters, for example one and a half meters. The upper retaining structure 14 has a central portion consisting of a first inner ring 24 fitted at least partially in the upper end 20 of the hollow body 12, eight radial portions consisting of first branches 26 which extend radially from the first inner ring 24 and are offset relative to each other by an angle close to 45 °, these first branches 26 being also secured to a first outer ring 28, and octahedral shape. This first outer ring 28 constitutes in particular means for reinforcing the rigidity of the upper retaining structure 14.

The first branches 26 each have a free end 30 and a first arcuate recess 32 near the free end 30. This first arcuate recess 32 is oriented towards the lower end 22. It is found on the Figure 3A , the frame 10 comprising the hollow body 12 and the upper retaining structure 14; the axial section plane III-III intersecting two diametrically opposed first branches 26, their respective arc recess 32, symmetrical with respect to an extremum 34 and symmetrical with respect to each other vis-à-vis the axis of symmetry A. Moreover, the first arcuate recesses 32 are spaced apart from the hollow body 12.

On the Figure 1 the first outer ring 28, of octahedral shape, which connects the first branches 26 at the level of the first arcuate recesses 32, is observed. Each of the eight substantially flat portions of the first outer ring 28 intersects a first branch 26 substantially perpendicularly. In addition, a second arcuate recess 36 is formed in each of these flat portions of first outer ring 28. This second recess 36 in arc of a curvature substantially identical to the first recess 32 has an extremum substantially coincident with the extremum 34 of the first recess arc 32.

Thus, the planar portions of the first outer ring 28 and their corresponding first branch 26 together define through their arcuate recesses 32, 36 a receiving zone 38 oriented towards the lower end 22, which reception zone 38 in turn defines a spherical ring whose function will be explained below.

Before that, we will describe with reference to the Figure 1 and at the Figure 3A , the lower retaining structure 16. The latter has a second inner ring 40 also fitted at least partially in the lower end 22 of the hollow body 12. It also has second legs 42 respectively symmetrical first branches 26 relative to a plane of symmetry intersecting the hollow body 12 perpendicular to mid-distance between the lower end 22 and the upper end 20. These second legs 42 are interconnected by a second outer ring 44. In contrast, the second legs 42 respectively present a notch 46 and not an arch recess like the first opposite branches 26. In contrast, the notch 46 has a first portion located near the second inner ring 40 substantially symmetrical to a first arcuate recess portion 32 from the extremum 34 towards the first inner ring and this, with respect to the plane of said symmetry intersecting perpendicularly the hollow body 12. However, a second portion of the notch 46 extends substantially radially towards the free end of the second branch 42.

In addition, the star struts 18 illustrated in detail on the Figure 1 , each define a mean plane substantially perpendicular to the hollow body 12 and they are formed of a circular ring in which are formed eight hemicircular recesses 48. The hemicircular recesses 48 of each of the circular rings are aligned with each other along a parallel axis to the axis of symmetry A hollow body 12 and which cuts each of the first and second branches 26, 42 opposite.

As illustrated by Figure 2 in each of the eight housings which extend between the upper retaining structure 14 and the lower retaining structure 16 and which are defined by the semicircular recesses 48 of the struts 18, the receiving zones 38 and opposite the notches 46 are engaged modular elements 50 forming a float. We find on this Figure 2 , the upper retaining structure 14 and the lower retaining structure 16 connected together by the hollow body 12, here masked by the modular elements 50. The latter are cylindrical in shape with a circular director, and they each have two opposite free ends, one upper free end 52 and a lower free end 54. Their diameter is between two and three meters, for example two meters forty, and their length is between thirty meters and forty meters, for example thirty-four meters.

The two free ends have a rounded shape defining a substantially spherical surface adapted to coincide with the receiving zone 38. Thus, the upper free end 52 of each of the modular elements 50 is engaged in the receiving zone 38, while the lower free end 54 is in abutment against the corresponding second branch 42, while the body 56 of each of the tubular elements 50 bears against the spacers 18 through their respective hemicircular recesses 48. It will be noted that, during assembly of the underwater buoy, the upper free end 52 of the modular elements 50 is first engaged in the receiving zone 38, the modular elements 50 being inclined with respect to the hollow body 12 and then , the tubular body 50 is folded towards the hollow body 12 resting in the spacers 18, the lower free end 54 abuts against the second legs 42. The modular elements 50 are held in this position or by 58 locking pieces reported at the free end of the second branches 42 which will be observed in more detail on the Figure 3A or by a buoy bridle shown which surrounds and encloses in the vicinity of the lower retaining structure 16 the eight modular elements 50.

In addition, and according to yet another embodiment, the modular elements 50 are maintained in support in the spacers 18, independently of each other, thanks to independent spacer flanges, which clamp the modular elements 50 in their corresponding hemicircular recesses 48. The strut flanges are mounted on each of the projecting ends of the struts 18 and are adapted to be connected to another contiguous end projecting around a modular element 50.

Moreover, in a particular embodiment of the invention illustrated on the Figure 3A , the upper free end 52 has an axial slot 64 in which is engaged an extension 66 projecting planar portions of first outer ring 28; and this, at the second arcuate recess 36. In this way, the upper free end 52 of the modular elements 50 is perfectly integral with the upper retaining structure 14 because it is perfectly locked in motion in directions substantially parallel to the plane P means defined by the upper retaining structure 14. In addition, the lower free end 54 is blocked radially in translation by the locking member 58, while the body 56 of the modular elements 50 is locked in translation in one direction. perpendicular.

We will refer to the Figure 4 illustrating a top view of the underwater buoy according to the invention. There are eight modular elements 50 engaged in their housing, and the upper retaining structure 14 comprising the first inner ring 24, the first branches 26 and the first inner ring 28.

Thus, the submarine buoy represented is relatively easy to assemble, either before being embarked on a boat laying, or on the boat or directly in the water. Moreover, it presents here eight modular elements 50, but it could include only one on two, four modular elements 50. Thus, its buoyancy would be less.

The mounting of the underwater buoy is illustrated on the Figures 5A to 5C . First, two first modular elements 50 are extended horizontally and parallel to each other on supports 70 and spaced a predetermined distance. Then, as shown in Figure 5B , a hollow body 12 equipped with its spacers 18 is fitted on these first two modular elements 50. The latter are then secured to the spacers 18 by means of spacer flanges as mentioned above. Then, two new modular elements 50, illustrated on the Figure 5C are mounted on the hollow body 12 in the position diametrically opposed to the first two modular elements 50. Finally, the assembly, equipped with four modular elements 50, is first tilted on two first modular elements 50 extended on supports identical to the supports 70 as illustrated in Figure 5A and located along these supports 70, and two other modular elements 50 are then installed on the last two remaining locations on the hollow body 12.

Then, the upper and lower retaining structures 14 and 14 are mounted at the ends of the hollow body 12.

As represented on the Figure 3A , the underwater buoy according to the invention is attached to a tubular pipe 60 for the transport of hydrocarbons via a clamping flange 62. In this way, the tubular pipe 60 is kept suspended from the buoy under -marine which tends to drag it towards the S surface in an underwater area below the surface. In addition, the tubular pipe 60 is connected to a flexible tubular pipe 63 which passes through the underwater buoy and escapes from above over the upper retaining structure 14 to then reach a surface installation.

Thus, the tensile forces to exert on the tubular pipe 60 can be adapted by adjusting the number of modular elements 50 to the armature 10.

According to another embodiment not shown, the tubular pipe 60 is connected to the underwater buoy via a frame itself suspended from the lower retaining structure 16, and the tubular pipe 60 is connected to a flexible tubular pipe that no longer crosses the underwater buoy but circumvents it to reach a surface installation.

According to an alternative embodiment of the invention shown on the Figure 3B and in said another embodiment, the aforementioned hollow body is replaced by a succession of six independent cylindrical floats, four identical 72, 74, 76, 78 and two end 80, 82, stacked on each other. In addition, the modular elements forming floats are here respectively replaced by two modular half-elements 84, 86, adjusted in the extension of one another. In this way, by substituting the hollow body for the independent cylindrical floats 72, 74, 76, 78, 80, 82, the overall buoyancy of the underwater buoy is increased. Moreover, and with equal buoyancy, this also allows in certain particular embodiments, to reduce the size of the modular elements. In addition, the increase in the number of floats decoupled from each other, eliminates the risk of deterioration of one of them. The cylindrical independent floats 72, 74, 76, 78, 80, 82, however, are adapted to receive water inside to be able to immerse the underwater buoy, while the modular half-elements are sealed and do not receive no water. This water cylindrical independent floats is then likely to be evacuated to be able to give the buoy underwater all its buoyancy. In order to ensure the water filling of the independent cylindrical floats 72, 74, 76, 78, 80, 82, the latter are respectively equipped in their base, with a first opening extended by a first conduit. The first conduits of all cylindrical floats independent 72, 74, 76, 78, 80, 82, converge to a common filling valve. In order to substitute a gas and in particular nitrogen for the water of independent cylindrical floats 72, 74, 76, 78, 80, 82, they respectively have an upper opening extended by a second duct. The second conduits converge in turn towards a common nitrogen inlet valve.

According to another aspect, the subject of the invention relates to a method of installing a rising submarine column for transporting hydrocarbons between a seabed and a surface, by means of an underwater buoy with elements. modular and / or independent cylindrical floats, as described above. The method being of the type according to which: anchoring a bottom installation on said seabed; providing a tubular conduit having a connecting end to be connected to said downstream installation and an opposite end equipped with a submersible float submarine buoy; then, the entry of water inside said submergible floats is authorized to immerse said underwater buoy and said tubular pipe in line with said bottom installation, while said underwater buoy and said buoy are retained. conducted by a suspension line from a surface vessel, said suspension line supporting tensile forces corresponding to the weight of said underwater buoy and said pipe; a traction cable is then provided and return means are installed on said downstream installation so as to be able to connect said traction cable to said connection end and to drive said cable through said return means and simultaneously said connection end towards said downstream installation; according to the invention, hooking a draft buoy immersed in said traction cable to exert additional traction forces on said suspension line; then a gaseous fluid is substituted with the water of said immersible floats to compensate, on the one hand, the traction forces corresponding to the weight of said underwater buoy and of said pipe and, on the other hand, at least a part of the traction forces additional; and, finally, said pulling buoy is tethered to said bottom installation and said suspension line is progressively released so that said bottom installation takes up said additional traction forces exerted by the pull buoy, while said underwater buoy said other part exerts additional traction forces on said pipe to maintain it vertically.

Thus, according to this other aspect the implementation of the submerged draft buoy, that is to say between the bottom and the surface, and more precisely near the bottom, to attach to the towing cable and then the release, allows to exert additional traction forces on said suspension line. Indeed, once released, the pulling buoy, which then contains a gaseous fluid lighter than water, pulls on the pulling cable which has the opposite effect, thanks to the return means on the end of connection of the pipe, and thus on the line of suspension that joins the surface building. Thus an additional traction force is exerted on the suspension line in excess of the own weight of the pipe and the underwater buoy.

Then, by mooring said draft buoy to said bottom installation and then releasing or progressively unwinding said line of suspension from the surface building, said underwater buoy and said tubular pipe gradually descend to the bottom installation, because the The pulling cable is driven through the return means via the pulling buoy which is driven to the surface. The latter, however, is retained by the mooring which connects it to the underground installation. From this moment, the forces exerted on the line of suspension, between the underwater buoy and the surface building, are canceled out. The advantage of such an arrangement lies precisely in that, as soon as the forces exerted on the suspension line tend to zero, and the surface building, for example, is driven by the swell in one direction vertical opposite the seabed, the efforts then exerted on the entire chain, suspension lines, buoy underwater, pipe and traction cable, then reverberate on the buoy which is then driven to the seabed. This makes it possible, of course, to preserve all the elements of the whole of the aforementioned chain, since the pull cable is not anchored to the seabed, as is the case according to the prior art.

Advantageously, said gaseous fluid, lighter than water, is substituted for the water of said immersible floats to compensate for the traction forces corresponding to the weight of the underwater buoy and substantially at half of said additional traction forces exerted by the intermediate of the draw buoy.

In addition, according to a particular embodiment of the invention, for connecting the connection end to said bottom installation, said pulling buoy is released from said bottom installation so that said pull buoy back to said surface. so as to drive the opposite end, said connection end to said downstream installation. To do this, damping receiving means are provided, from the connecting end when approaching downwards, from the bottom installation.

Claims (9)

1. Underwater buoy with modular members (50) intended to suspend a tubular duct (60) between a seabed and a surface, said buoy comprising a frame (10) and a plurality of modular members (50) forming floats adapted to be mounted in said frame, said modular members extending longitudinally between two opposite modular member ends (52, 54), said frame having a longitudinal hollow body (12) intended to receive said extended tubular duct and retaining means (14, 16, 18) mounted radially on said hollow body to hold said modular member (50) substantially parallel to said hollow body and around said hollow body;
   characterized in that said retaining means comprise two facing retaining structures (14, 16) spaced longitudinally from each other on said hollow body (12), said retaining structures having respective pluralities of receiving areas (38, 46) each adapted to receive a modular member end (52), each modular member (50) being of cylindrical shape with a circular directrix to resist hydrostatic pressure;
   and in that said retaining structures (14, 16) are held in a fixed position relative to each other in a position in which said receiving areas (38, 46) face each other so as to trap at least one modular member (50) when said opposite ends (52, 54) of said at least one modular member are engaged in respective facing receiving areas (38, 46).
2. Underwater buoy according to claim 1, characterized in that said retaining means further include spacers (18) mounted on said hollow body (12) to hold said modular members (50) away from said hollow body.
3. Underwater buoy according to claims 1 and 2, characterized in that said spacers (18) have respective semicircular recesses (48) to receive said modular member (50) .
4. Underwater buoy according to any of claims 1 to 3, characterized in that said retaining structures have a central portion (24, 40) fastened to said hollow body (12) and radial portions (26, 42) in which said receiving areas (38, 46) are provided.
5. Underwater buoy according to claim 4, characterized in that said retaining structures have eight radial portions (26, 42) diametrally opposed in pairs in which eight respective receiving areas (38, 46) are provided.
6. Underwater buoy according to any of claims 1 to 5, characterized in that said retaining structures define a mean plane P that is substantially perpendicular to said hollow body (12) and at least one of said retaining structures (14) is equipped with complementary immobilizing means in said receiving areas (38) to immobilize said modular member (50) in all directions substantially parallel to said mean plane.
7. Underwater buoy according to claim 6, characterized in that said at least one of said retaining structures (14) has reinforcing means (28) for increasing the stiffness of said at least one of said retaining structures.
8. Underwater buoy according to claim 7, characterized in that said hollow body (12) has in the vicinity of the other of said retaining structures (16) means (62) for attachment to said tubular duct (60).
9. Underwater buoy according to claim 8, characterized in that said other of said retaining structures (16) includes means (58) for locking said modular members (50).

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